Most researchers believe that people who are blind from birth or who become blind in infancy do not see in their dreams. They do not retain visual imagery because it was never acquired in the first place.

However, those blinded in childhood, adolescence, young adulthood, or afterwards usually do see in their dreams. "They often retain visual imagery in their waking life and in their dreams," according to Drs Nancy Kerr of the Department of Psychology at Oglethorpe University and G. William Domhoff of the Department of Psychology at the University of California at Santa Cruz.

They write in the December 2004 issue of Dreaming that "individuals blinded before the age of about five report no visual imagery in dreams as adults, whereas those blinded after about the age of seven are likely to retain visual imagery in dreaming".

This conclusion is based upon four sleep laboratory studies conducted between 1966 and 1999. According to the Royal National Institute of the Blind in London: "Dreams are experienced in the same way as life is lived. If someone loses their sight, they will dream of events during the days when sight was available in visual terms. If dreams are about recent events when sight was not used, sensations will be in terms of sound, smell, texture, and so on." A person dreams as they live.

Can people have the same dream at the same time?

It is called simultaneous dreaming. This occurs when two or more people have the same dream. The dream need not occur at the same time to qualify as a simultaneous dream. But sometimes this happens too. There are no scientific studies of simultaneous dreaming.

However, there are a few anecdotal reports of simultaneous dreaming on the internet. It is usually mentioned in relationship to lucid dreaming. Lucid dreaming is the conscious perception of one's state while dreaming with the intended effect of having clearer dreams and to be able to control, focus, and utilise dreams to improve one's life.

Are humans the only animals that dream?

Besides humans, other animals probably dream too. According to Dr Allan Hobson, a professor of psychiatry at Harvard Medical School, writing in the August 2003 issue of Discover: "Although it cannot be proved, it is reasonable to suppose that many animals see, hear, feel, and run in their sleep just as we do."

Most researchers agree that brain activity during dreaming functions to help keep body temperature stable during sleep. Body temperature stability during sleep is also necessary in mammals besides humans. There is also evidence that dreaming helps solidify memories. This would have a survival advantage in both humans and non-human animals. For these and other reasons, Dr Hobson concludes that it is logical to conclude that at least some animals probably do dream. Too bad they cannot tell us and remove all doubt. Perhaps they might some day? Dream on!

Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to [email protected]